This is a true spectrophotometric measurement of a N7 “neutral” gray is not simply a black-white mix, but an equal mixture of all the spectrum (r-o-y-g-b-i-v) colors.

Non-neutral grays, however, have unequal amounts of the spectrum colors, causing a cold or warm color shift under differing lighting conditions.
Typically paint used for the neutral surround conditions specified in Colour Standards.
Why is Neutral Grey specified and recommended for color viewing?
1. It eliminates “simultaneous color contrast”. For example, a red sample viewed on a blue background has an orange cast, while the same red viewed on a yellow background appears slightly purple. For the eye to see color accurately, it is imperative that the surround environment be chromatically neutral.
2. It minimizes “colour pollution” of viewing areas caused by reflections from chromatic surfaces. When D50 or D65 standard illumination is reflected from colored walls, etc., it's colour quality changes so it's no longer “standard”. The application of a neutral grey to chromatic surfaces will eliminate such color pollution by providing spectrally neutral surfaces around the viewing area.